Summaries for Patients|21 August 2007

Long-Term Use of Selenium Supplements and Risk for Type 2 Diabetes
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The summary below is from the full report titled “Effects of Long-Term Selenium Supplementation on the Incidence of Type 2 Diabetes. A Randomized Trial.” It is in the 21 August 2007 issue of Annals of Internal Medicine (volume 147, pages 217-223). The authors are S. Stranges, J.R. Marshall, R. Natarajan, R.P. Donahue, M. Trevisan, G.F. Combs, F.P. Cappuccio, A. Ceriello, and M.E. Reid.

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What is the problem and what is known about it so far?

Selenium is a mineral that is required in very low doses for the body to function normally. It is an antioxidant, meaning that it prevents oxygen from damaging cells. Although most people get enough selenium in their diet, selenium is included in many multivitamins and is sold as a supplement itself. Many people take selenium supplements to stay healthy. Some research suggests that selenium supplements can improve the way the body handles sugar and might prevent some complications of diabetes. However, other research suggests that selenium supplementation has no effect on diabetes or health.

Why did the researchers do this particular study?

To see whether taking selenium supplements prevents diabetes.

Who was studied?

1202 people with skin cancer other than melanoma who were seen in dermatology clinics in areas of the United States where people tend to have low blood levels of selenium. None of the participants had diabetes.

How was the study done?

The researchers measured participants' blood selenium levels. They then randomly assigned the participants to take selenium supplements (200 micrograms) or placebo pills. They followed the participants over an average of 7 years to see who developed diabetes. They then compared the number of people with diabetes in the 2 groups.

What did the researchers find?

More people who took selenium developed diabetes than those who took placebo pills. The risk for diabetes seemed to be higher in people who had higher blood selenium levels at the start of the study.

What were the limitations of the study?

The researchers relied on participants' reports that they developed diabetes and did not confirm those reports with measures of blood sugar. The findings apply to the specific dose of selenium used in the study. Participants tended to be older and white, so the findings might not apply to younger people and those of other races.

What are the implications of the study?

Selenium supplements appear to increase the risk for diabetes. Although the findings need to be confirmed, long-term selenium supplementation should not be viewed as harmless and a possibly healthy way to prevent illness.

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